1. Field of the Invention
This invention relates to fuel injection control apparatus and method for a direct injection internal combustion engine, which increases the quantity of fuel injected when a decrease in engine speed is detected.
2. Description of the Related Art
Immediately after a cold start of an engine, fuel does not vaporize readily because some of the injected fuel adheres to the cylinder walls. As a result, the combustion state of the internal combustion engine may become unstable and the engine speed may drop. Therefore, a conventional fuel injection control apparatus for an internal combustion engine is configured to compensate for any detected decrease in engine speed by injecting more fuel than is normally injected to increase engine output, thereby suppressing the decrease in engine speed (e.g., see Japanese Patent Publication No. 8-33123).
In fuel injection control of an internal combustion engine, the fuel injection quantity must be set in advance, before the fuel is actually injected from a fuel injection valve. Therefore, a fuel injection signal indicative of the fuel injection quantity must be generated and input beforehand to a drive circuit of the fuel injection valve. Moreover, after the fuel injection quantity is set, engine control parameters such as the ignition timing and the like are set based on that fuel injection quantity.
As described above, the timing at which the injection quantity is set (hereinafter referred to as the “injection quantity setting timing”) and the actual timing at which the fuel is injected (hereinafter referred to as the “actual fuel injection timing”) must be set to different timings. The difference in timing poses a significant problem if the decrease in engine speed is to be suppressed quickly. That is, once the injection quantity has been set for a particular cylinder, the injection quantity cannot be increased for that fuel injection to compensate for any detected decrease in engine speed, even if a fuel injection has not yet been executed in that cylinder. Therefore, the quantity of fuel injected can only be increased for a cylinder in which an injection quantity is yet to be set after a decrease in engine speed is detected. If the engine speed drops further during this time, the likelihood of the engine stalling increases. In view of this, with the conventional injection quantity increase method, after a decrease in engine speed has been detected, that decrease is unable to be suppressed quickly, so there still remains room for improvement here.